In parts of Africa, residents and missionaries take garlic (Allium sativum) instead of chloroquine as a means of preventing malaria because it is believed that the odor of garlic exuded through the pores acts as a mosquito repellent thus preventing Anopheles vectors from biting. Previously we reported that Aedes aegypti mosquitoes fed on garlic-laced blood regardless of the concentration; whereas Anopheles stephensi females were significantly affected with the degree of repellency directly proportional to the garlic concentration. In an in vivo study a 300 mg garlic tablet was fed each day to a guinea pig throughout the study. The garlic-fed guinea pig and another guinea pig serving as a control were anesthetized, the ventral surface of both animals was shaved, and then each was coated with a different colored fluorescent powder before placing them on the top of an 8 cubic foot mosquito cage. It could be determined which animal each killed mosquito fed upon by shining a UV light on the mouthparts and observing the color that fluoresced. For 1,500 Aedes aegypti, chi-square analysis showed no significant difference between the number that engorged on the garlic-fed guinea pig (43%) versus the control animal (57%), whereas this comparison was highly significant for the Anopheles stephensi (34% versus 66%, respectively). Also, the differences in blood feeding behavior between the two mosquito species was highly significant suggesting that garlic did have a definite repellent effect against Anopheles.